The number and shape of Langerhans’ cells (LC) were studied by determining cytoplasmic formaldehyde-resistant ATPase activity in whole mounts of normal and meta-plastic human cervical epithelium. In normal epithelium the number of LC per square millimeter was 52.75 ± 2.21. A similar number was found in completely differentiated metaplastic squamous epithelium (49.11 ± 2.42), but their shape was different with less branching processes. When metaplasia was still incomplete, and numerous mucous cells remained, no LC were present. On the basis of these results it is speculated that mucous cells provide a negative chemotactic stimulus which prevents migration of LC into metaplastic epithelium. When the latter is completely squamous it is repopulated by LC in a fashion similar to normal squamous epithel